I must side with Peter Harris. Plants certainly do secrete compounds into
the rhizosphere and they don't just do this via cell loss. At least this is
my understanding. However, having said that I guess it may not have been
proven that many of the compounds "secreted" have not come from the contents
of degraded cells. I don't see why this is not a form of secretion though.
Exocytosis by a whole cell rather than a secretory vesicle. In practice the
compounds are called root-exudates such as those stimulating germination of
root parasites such as Striga spp.
David C. Logan
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